Process for the treatment of cast bars in continuous casting plants

ABSTRACT

The invention relates to a process for the treatment of cast bars in continuous casting plants comprising a vertical mould, a curved and then horizontal supporting and guiding portion and a drawing and shaping stand with an adjustable roll gap, in which, in order to avoid any piping in the end part of the bar, the withdrawal speed is increased after casting is finished and the rear end of the bar is sealed so that the sump tip of the liquid bar core is shifted forward at least to the roll gap and a densening pressure is exerted upon the bar by narrowing said roll gap. With this process the output capacity of high capacity continuous casting plants is considerably improved.

United States Patent [1 1 Schoffmann July 24, 1973 PROCESS FOR THE TREATMENT OF CAST BARS IN CONTINUOUS CASTING PLANTS.

[75] Inventor: Rudolf Schoffmann, Linz, Austria [22] Filed: June 28, 1971 [21] Appl. No.: 157,093

[30] Foreign Application Priority Data l/l970 Tarmann et al. I/l970 Tarmann et al. l64/76 OTHER PUBLICATIONS Continuous and Pressure Casting, published by Association of Iron and Steel Engineers, Pittsburgh, Pa., 1964. Page 14.

Primary Examiner-R. Spencer Annear Attarney-Granville M. Brumbaugh et al.

[57] ABSTRACT The invention relates to a process for the treatment of cast bars in continuous casting plants comprising a vertical mould, a curved and then horizontal supporting and guiding portion and a drawing and shaping stand with an adjustable roll gap, in which, in order to avoid any piping in the end part of the bar, the withdrawal speed is increased after casting is finished and the rear end of the bar is sealed so that the sump tip of the liquid bar core is shifted forward at least to the roll gap and a densening pressure is exerted upon the bar by narrowing said roll gap. With this process the output capacity of high capacity continuous casting plants is con siderably improved.

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PROCESS FOR THE TREATMENT OF CAST BARS IN CONTINUOUS CASTING PLANTS The invention relates to a process for the treatment of cast bars in continuous casting plants comprising a vertically arranged, water-cooled mould, a supporting and guiding portion joined to said mould and designed to be curved at first and then horizontal in which the cast bar having a liquid core is further cooled and in which the drawing speed of the bar during casting is chosen in a manner that the bar has solidified completely when leaving the horizontal supporting and guiding portion, and a drawing and shaping stand with an adjustable rolling gap arranged after the horizontal supporting and guiding portion.

Continuous casting plants comprising a supporting and guiding portion which is curved at first then changes into the horizontal line for a cast bar which has a still liquid core are already known from the U.S. Pat. No. 2,698,467 and from Stahl and Eisen 90 (1970), pages I53 to 161, Huttenwerksanlagen hochste Leistung, Planungsstand and Entwicklungsmoglichkeiten byMeinshausen. When the casting output is high a correspondingly long liquid core (sump, liquid phase) is formed in the bar so that the supporting and guiding portion supporting the bar shell has to become correspondingly long so that the bar is supported over the entire length of theliquid core and the ferrostatic pressure present in theliquid core is compensated and the bar is prevented from fattening. In order to maintain the advantage of low construction height in continuous casting plants with curved supporting and guiding portions it becomes necessary when operating with high casting speeds to provide for a correspondingly long horizontal supporting and guiding portion. When slabs are cast from steel, in the end part of the bar shrinkage cavities are formed, which is a disadvantage. The reason for this lies in the fact that the ferrostatic pressure in the liquid bar core decreases after drawing out of the bar end from the mould until it obtains the value zero when the bar runs through the horizontal supporting and guiding portion. As a result thereofa piping of considerable length is formed in the end part of the bar running out in horizontal direction so that this bar part cannot be utilized as a rule; hence high speed continuous casting plants with a horizontal supporting and guiding portion have no satisfactory yields.

The invention is aimed at increasing the yields of high capacity continuous casting plants with a horizontal guiding and supporting portion and, in a process of the kind described in the introduction, resides in that after termination of casting and covering of the bar end, in order to avoid any piping in the end part of the bar, by increasing the drawing out speed, the tip of the sump of the liquid bar core is shifted forward at least to the roll gap and in that a densening pressure is exerted upon the bar by narrowing the roll gap.

From the Austrian Pat. No. 187,251 a process for continuously casting pipe-free bars has become known, in which the bar, above the natural sump tip'of the liquid core is pressed together by rolls arranged after the mould to a degree that the inner walls of the already soliditied bar shell weld together in their borderlayers,

without however causing a change in their wall thickness and an extension of the yet plastic marginal zone of the bar. This process, however, has not been generally accepted inpractice because with this process it is not possible to prevent piping in the end part of a slab bar, which solidifies in the horizontal line. The same applies to the process described in the Austrian Pat. No. 266,362 in which the cast bar is immediately shaped by means of a shaping device which is arranged between the continuous casting mould and the natural sump tip and causes a shortening of the length of the liquid phase. This known process for cogging down a cast bar wth a liquid core is applicable to advantage only in the production of billets; the advantage lies in the fact that the mould cross-section may be kept relatively large so that the operating conditions during casting are essentially improved. Despite a great casting cross section, only relatively small billet cross sections may be produced owing to the shaping of the cast bar. In casting of broad steel slabs the process according to the mentioned Austrian Pat. No. 266,362 has not been employed so far, for in continuous casting plants for slabs the solidified bar is drawn out either without any further shaping at all or a small degree of shaping is applied on the broad side of the bar.

When the process according to the invention is applied to steel bars having a rectangular cross section it is advantageous to create the densening pressure by cogging down the cast bar, the reduction of the bar thickness amounting from 10 to 30 mm, preferably from 15 to 20 mm.

According to a further feature of the invention the sump tip of the liquid bar core is shifted forward beyond the vertical plane laid through the roll gap by 0.5 to 2 mm before the densening pressure is applied, by increasing the drawing out speed of the bar.

In order that the invention may be more fully understood an embodiment thereof shall now be explained with reference to the accompanying drawing.

FIG. 1 is a simplified, schematical vertical sectional view of an end part of a cast bar which after termination of casting is drawin out from a continuous casting plant; thereby the whole cast bar is cogged down.

FIG. 2 is a similar representation as FIG. 1 in which the end part of the bar in which the core is yet liquid is drawn out with increased speed as it runs through the horizontal supporting and guiding portion.

FIG. 3 is an analogous representation as FIG. 2 for a case in which only the end part of the bar is cogged down but not the whole bar.

FIG. 4 is a diagram of the current consumption of the drive motors for the drawing and shaping stand in dependence on the drawing out speed of the cast bar.

In FIG. 1 numeral 1 is a water-cooled continuous casting mould from which the cast bar 2 with an already solidified casting shell 3 and a liquid core 4 issues and is further cooled in a supporting and guiding portion of the continuous casting plant. This supporting and guiding portion is provided with a plurality of rollers 5 arranged at both sides of the bar 2, and some pairs of driving rolls 6, 7 arranged in between. A further pair of driving rolls 8 is built in behinda pair of rolls 9 of a combined drawing and shaping stand arranged behind the'supporting and guiding portiomNumeral 10 is the tip of the liquid core 4. During casting a plane 11 laid through the liquid phase tip 10 has a distance L from a plane 12 laid through the casting level, measured along the bar axis, L amounts to about 23 m with a mould cross section of mm- X 1,500'mm when deep drawing steel killed with aluminium is cast at a steel temperature of l,550 C measured in the tundish and a drawing out speed of 2 m/min. Below the continuous casting mould 1 a roller guide is provided which is at first vertical for about 2 m but in the plane 13 slowly becomes a circular roller guide with the radius R; with continuous casting plants for slabs in which the mould has the above mentioned dimensions R amounts to about 8 to 10 m. Numeral 14 denotes a vertical plane laid through the pair of driving rolls 6 which plane measured along the bar axis is about m remote from the plane 12 laid through the casting level. The horizontal supporting and guiding portion is about 10 m long and extends from the plane 14 to the last pair of rollers 5 in front of the pair of rolls 9. Numeral 15 is a vertical plane laid through the pair of rolls 9 which is arranged at a distance of 1.5 m from the last pair of rollers 5.

During casting the 180 mm thick solidified bar 2 is cogged down over its entire extension by a total of l5 mm to 165 mm by the pair of rolls 9 at a drawing speed which remains essentially uniform; the cogged down bar is denoted with 16. When casting is terminated a cover is formed at the bar end bysplashing water ontothe solidifying bar; during drawing the thickness of this cover is increased by further cooling in the arcshaped supporting and guiding portion; in FIG. 2 this thickened cover is deonted with numeral 21. After the bar end is drawn out from the upper part of the areshaped supporting and guiding portion or before the ferrostatic pressure in the liquid core 4 has reached the value zero, respectively, the drawing out speed is increased. This causes a theoretical shifting of the liquid phase tip. 10 from the plane 11 to the plane 17 by the distance S which is to amount to about 4 m; in the present case the distance between the planes l5 and 17 amounts to about 0.5 m; in the drawing this distance is exaggerated for a better understanding. Since a drawing out speed of 2 m/min corresponds to a length L of the liquid core 4 of 23 m, the mentioned steel quality has a solidifying time of l 1.5 min. If as indicated the liquid phase tip 10 is to be shifted by a distance S of 4 m, the length of the liquid core 4 has to be increased to 27 m, which may be achieved by increasing the drawing out speed from 2.0 to 2.35 m/min. At this increased drawing out speed the contour 18 shown in dotted lines in FIG. 2 of the liquid core 4 would be obtained which ends in the plane 17. However, owing to the shaping obtained by the pair of rolls 9 the liquid phase tip 19 is actually shifted in front of the plane 15, whereby a densening pressure is applied on the liquid core 4 so that in the last part of the bar the formation of cavities or cracks is avoided. The liquid core 4 which is closed at the bar end by the cover 20 or 21, respectively, thus solidifies over its total length under pressure. Thus, also the last part of the bar'has the same quality as the rest of the bar. The pressure acting on the liquid core 4 may easily be absorbed by the cover 20 or 21, so that no liquid steel may erupt.

In FIG. 3 a variation of the process is described: the cast bar 2 is not shaped at first so that the thickness of the solidified bar 22 corresponds to the thickness of the case bar 2. Only after the drawing out speed is increased cogging down is started so that a somewhat thinner end of the cast bar 23 is obtained; it is likewise free from cavities.

There is no problem in increasing the drawing out speed; it is regulated, e.g., by means of the current consumption of the driving motors for the pair of rolls 9. In FIG. 4 the bar drawing out speed v in m/min is plotted on the abscissa and the current consumption of the motors in Ampere on the ordinate. With increasing drawing out speed the liquid phase tip 10 is shifted in direction towards the plane 15 laid through the roll gap so that the shaping work is increased which is expressed by a reduced current consumption corresponding to the curve 24. As soon as the liquid phase peak 10 has reached the plane 15, the bar shell 3 is fattened in front of the rolls 9 so that shaping is rendered more difficult; experience has shown that this is expressed by an increase in the current consumption corresponding to the curve 25. Thus the deepest value in the course of the curves 24, 25 indicates with relative accuracy the value 26 for the drawing out speed to be adjusted to for the desired position of the liquid phase tip in relation to the roll gap.

What is claimed is:

1. A process of producing a cast bar in a continuous casting plant from a pre-determined amount of metal, the bar being cast continuously through a vertically arranged water-cooled mould in a downwardly direction, the cast bar having a solidified outer section and a liquid core section, the cast bar being guided first through a curved supporting means and then through a substantially horizontal supporting means, the rate of travel of the cast bar being adjusted during casting so that the cast bar is completely solidified when leaving the horizontal supporting means, and the solidified cast bar being subjected to a drawing and shaping operation in a roll stand with an adjustable roll gap, the improvement comprising the steps of sealing the end of the cast bar in the mould when the pre-determined amount of metal is exhausted, increasing the rate of travel of the cast bar in the two supporting means to shift the forward most tip of the liquid core of the bar to a downstream position at least at the roll gap, and adjusting the roll gap to exert a densening pressure upon the cast bar.

2. The process set forth in claim 1 wherein the cast bar produced by the continuous casting plant has a rectangular cross section and the roll gap is adjusted so that the thickness of the cast bar is reduced approximately 10 to 30 mm.

3. The process set forth in claim 1 wherein the tip of the liquid core is shifted 0.5 to 2.0 m downstream of the rolll gap.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa tent No. 3: 7 7, 66 4- Dated y 973 Inventor(s) Rudolf Schoffmann It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"1 Col. 2, line 31, "2 mm" should be --2 m--; Col. 2 line 38, "'drawin" should read --drawr 1--'; Col. 3 line 26*, "deonted" should read -denotedg Col. line t, "case" should read --cast--,-

Col. line 16, "increased" should read --d ecreased--; and (301. line 56, "r0111" should read -roll--.

Signed and sealed this .25t h day of December 1973.

(SEAL) Attest:

EDWARD M.FLETCHER JR. RENE D. TEGTMEER I Attesting Officer Acting Commissloner of Patents 

1. A process of producing a cast bar in a continuous casting plant from a pre-determined amount of metal, the bar being cast continuously through a vertically arranged water-cooled mould in a downwardly direction, the cast bar having a solidified outer section and a liquid core section, the cast bar being guided first through a curved supporting means and then through a substantially horizontal supporting means, the rate of travel of the cast bar being adjusted during casting so that the cast bar is completely solidified when leaving the horizontal supporting means, and the solidified cast bar being subjected to a drawing and shaping operation in a roll stand with an adjustable roll gap, the improvement comprising the steps of sealing the end of the cast bar in the mould when the pre-determined amount of metal is exhausted, increasing the rate of travel of the cast bar in the two supporting means to shift the forward most tip of the liquid core of the bar to a downstream position at least at the roll gap, and adjusting the roll gap to exert a densening pressure upon the cast bar.
 2. The process set forth in claim 1 wherein the cast bar produced by the continuous casting plant has a rectangular cross section and the roll gap is adjusted so that the thickness of the cast bar is reduced approximately 10 to 30 mm.
 3. The process set forth in claim 1 wherein the tip of the liquid core is shifted 0.5 to 2.0 m downstream of the rolll gap. 